During last many decades there is frightening increase in the use of insecticides which is a dangerous situation for the humans mainly due to the residual effect of the pesticides in crops/vegetables. Chlorpyrifos (CPF), an organophosphate pesticide is being extensively used in the field of agriculture and veterinary science. In the mammals and birds, the chlorpyrifos intoxication is due to the inhibition of acetylcholine esterase which is responsible for the degradation of the neurotransmitter acetylcholine, and the resultant cholinergic over stimulation leads to the manifestations of neurotoxicity. In Pakistan, the water quality in many areas is poor and the contamination with arsenic is one of the major causes of deterioration. Arsenicosis is one of the major clinical syndromes present in Pakistan due to drinking arsenic rich water. Polyphenolic grape seed extract (PGE) is an antioxidant nutritive supplement having broad spectrum properties and can be used to ameliorate the effects of arsenic and chlorpyrifos. The present study was planned to document the all possible toxicological effects of organophosphate, arsenic and their amelioration with polyphenolic grape seed extract in broiler chicks. For this purpose, three experiments were conducted. The 1st experiment was conducted only with chlorpyrifos on 120 day-old broiler chicks divided in to 4 equal groups to check the toxicopathological effects. The groups were allotted according to the doses of the chlorpyrifos 5, 10, 20mg/kg BW and control. The selective doses of chlorpyrifos were given for two weeks and for the rest of experiment the birds were fed without chlorpyrifos, i.e., normal feeding. The clinical signs observed during the experiment were salivation, lacrimation, frequent defecation, gasping, tremors and convulsions. In the present study decreased feed intake in dose dependent manner was observed. The changes in body weight were also dose dependent. The changes in blood parameters induced by chlorpyrifos were noted in the present experiment. A significant decrease in the values of total erythocytic count, hemoglobin, packed cell volume and total leukocytic count as compared to control were observed in treatment groups during the treatment period. A significant increase in aspartate amimotransferase, alanine aminotransferase, total proteins and total albunmin levels were xxiv observed in the treated groups as compared to control during the treatment period. Nonsignificant results were observed in total globulin as compared to control during the experiment. Significantly lower level of acetyl cholinesterase was observed in blood, serum and plasma during the treatment period. The relative weights of liver, kidney and thymus were significantly higher in treated groups as compared to control. However, significant decrease in relative weight of bursa was observed in treatment groups as compared to control. Non-significant difference in relative weight of intestine, brain and spleen among various groups was observed. Grossly, mild hemorrhages were observed in liver treated with different doses of chlorpyrifos. In kidneys, mild to moderate congestion and swelling were observed in treated groups. Microscopically, tubular epithelial necrosis and detachment of epithelium from basement membrane were noticed. Moderate necrotic changes and vacuolar degeneration in lymphoid follicles were observed in bursa of Fabricius. In thymus, moderate to severe necrosis, congestion and vacuolar degeneration were observed. In spleen, mild to moderate congestion and necrosis were observed. Liver showed mild congestion, degenerative changes, congestion and cytoplasmic vacuolation. Necrosis and disruption of the epithelium of villi were observed in the intestine. Mild to moderate necrotic changes were observed in the brain. In 2nd experiment, effects of concurrent feedings of organophosphate and arsenic were recorded in 150 day-old broiler chicks which were divided in to five equal groups. The groups were allotted different doses of the chlorpyrifos (5mg, 10mg and 20mg/kg BW) and arsenic (50mg/kg BW), i.e., 5mg +arsenic 50mg, 10mg + arsenic 50mg, 20mg + arsenic 50mg, arsenic 50mg/kg BW and control. Clinical signs observed during the second experiment were almost similar as described in experiment one. However, in the treated groups when arsenic was administered in combination with chlorpyrifos, the severity of clinical signs were high in a dose dependent manner as compared to control. Arsenic alone and in combination with chlorpyrifos resulted in reduced feed intake and body weight as compared to control. In the present study, decrease in total erythrocytic count, hematocrit, hemoglobin and total leukocytic count by exposure of arsenic alone or in combination with chlorpyrifos was observed. Increase in total proteins and albumin was observed in high dose group as compared to control. However, non-significant effect xxv on globulin was observed in this experiment. Increase in the levels of aspartate aminotransferase and alanine aminotransferase were observed in high dosed groups in combination of arsenic and chlorpyrifos as compared to control and other groups. Similar findings were observed in acetyl cholinesterase levels in blood, serum and plasma as in experiment one. The relative weight of kidney was higher in groups fed higher levels of arsenic and chlorpyrifos as compared to control and there was no change observed considerably in arsenic treated group. The increase in the relative weight of intestine was also observed in highest dose combination group as compared to control, while no change was observed considerably in other groups in this experiment. The decrease in the relative weights of bursa and thymus was observed as compared to control and no considerable change was observed in the relative weights of spleen and brain in this experiment. Grossly and microscopically, lesions of similar kind were observed in all organs as in experiment one. In ameliorative effect of polyphenolic grape seed extract was recorded in last experiment. For this purpose 360 day-old broiler birds were divided in to twelve equal groups. The groups were allotted different doses of the chlorpyrifos (10mg and 20mg/kg BW), arsenic (50mg/kg BW) and polyphenolic grape seed extract (80mg/kg BW), i.e., 10mg, 20mg, 10mg + arsenic 50mg, 20mg + arsenic 50mg, arsenic 50mg, PGE 80mg, PGE 80mg + 10mg, PGE 80mg + 20mg, PGE 80mg + arsenic 50mg, PGE 80mg + 10mg + arsenic 50mg, PGE80mg + 20mg + arsenic 50mg and control. In the present study, the treated groups when given in addition of polyphenolic grape seed extract showed decreased intensity of clinical signs as compared to other groups. The addition of polyphenolic grape seed extract in treatment groups (chlorpyrifos and arsenic) showed improved in feed intake. Over all, considerable increase was observed in erythrocyte indices in polyphenolic grape seed extract treated groups as compared to other groups, also there was considerable decrease in enzymes level except acetyl cholinesterase which was increased in groups treated with polyphenolic grape seed extract. In contrast to first and second experimental findings, increase or decrease in the relative weights of liver, kidney, bursa, brain, intestine, spleen and thymus was observed in the third experiment. This improvement in these parameters about the above said organs indicates the xxvi ameliorating effect of polyphenolic grape seed extract. Grossly and microscopically, the groups treated with polyphenolic grape seed extract showed considerably less degenerative changes as compared to other groups treated with chlorpyrifos alone or in combination with arsenic.